This application relates to a refrigerant system wherein a single variable speed control is selectively utilized to provide operation of different components within the refrigerant system at variable speeds.
Refrigerant systems are utilized in applications to change the temperature and humidity or otherwise condition the environment. In a conventional refrigerant system, a compressor delivers a compressed refrigerant to a heat exchanger, known as a condenser, which is typically located outdoors. From the condenser, the refrigerant passes through an expansion device, and then to an indoor heat exchanger known as an evaporator. In the evaporator, moisture may be removed from the air, and the temperature of air blown over the evaporator coil is reduced. From the evaporator, the refrigerant returns to the compressor. Of course, basic refrigerant systems are utilized in combination with many other optional features and in various design configurations.
Variable speed drives are known to vary a compressor operating speed. As the compressor speed is varied, the capacity of the refrigerant system is adjusted as well. Thus, for efficiency, occupant comfort, and flexible system control, it would be desirable to have the ability to operate not only the compressors but also several other components in a refrigerant system, such as fans or pumps, at a variable speed. It is also known to utilize separate and independent variable speed drives (or variable frequency drives) to control the operation of fans blowing air over the heat exchangers or pumps delivering liquid through secondary loops to these heat exchangers. Running a compressor at a variable speed provides an easy way to adjust system capacity. It is often desirable for capacity (sensible and latent) and a head pressure control to adjust the speed of fans or pumps associated with the same refrigerant system. In other words, it is desirable to run both a compressor and a fan at a variable speed.
On the other hand, variable speed drives are expensive. Having an independent variable speed control and drive at each component that would desirably be run at a variable speed would be very expensive. Further, if plural variable speed drives are utilized, the circuitry becomes complex, and undue amounts of space are required. Also, the variable speed controls may only be engaged during limited periods of time during unit operation. In the past, it was proposed to use a single variable speed drive in a system having multiple compressors, and utilize the variable speed drive to be selectively connected to each compressor motor on a needed basis. However, it has not been known to utilize a variable speed drive that can be selectively connected between a compressor motor and a fan motor.